This section provides background information related to the present disclosure which is not necessarily prior art.
Articles of footwear conventionally include an upper and a sole structure. The upper may be formed from any suitable material(s) to receive, secure, and support a foot on the sole structure. The upper may cooperate with laces, straps, or other fasteners to adjust the fit of the upper around the foot. A bottom portion of the upper, proximate to a bottom surface of the foot, attaches to the sole structure.
Sole structures generally include a layered arrangement extending between a ground surface and the upper. One layer of the sole structure includes an outsole that provides abrasion-resistance and traction with the ground surface. The outsole may be formed from rubber or other materials that impart durability and wear-resistance, as well as enhancing traction with the ground surface. Another layer of the sole structure includes a midsole disposed between the outsole and the upper. The midsole provides cushioning for the foot and is generally at least partially formed from a polymer foam material that compresses resiliently under an applied load to cushion the foot by attenuating ground-reaction forces. The midsole may define a bottom surface on one side that opposes the outsole and a footbed on the opposite side that may be contoured to conform to a profile of the bottom surface of the foot. Sole structures may also include a comfort-enhancing insole or a sockliner located within a void proximate to the bottom portion of the upper.
The metatarsophalangeal (MTP) joint of the foot is known to absorb energy as it flexes through dorsiflexion during running movements. As the foot does not move through plantarflexion until the foot is pushing off of a ground surface, the MTP joint returns little of the energy it absorbs to the running movement and, thus, is known to be the source of an energy drain during running movements. Embedding flat and rigid plates having longitudinal stiffness within a sole structure is known to increase the overall stiffness thereof. While the use of flat plates stiffens the sole structure for reducing energy loss at the MTP joint by preventing the MTP joint from absorbing energy through dorsiflexion, the use of flat plates also adversely increases a mechanical demand on ankle plantarflexors of the foot, thereby reducing the efficiency of the foot during running movements, especially over longer distances.
Corresponding reference numerals indicate corresponding parts throughout the drawings.